Technical Field
The present invention relates to a road surface information acquisition apparatus for acquiring road surface information about a carpool lane based on a captured road surface image forward of a vehicle.
Background Art
Various assistance apparatuses have been proposed that are configured to acquire road surface information of a road on which a vehicle is travelling to assist a driver in driving the vehicle. For example, an assistance apparatus for conducting lane keeping control recognizes a lane width from a captured image of a road on which a vehicle is travelling and assist the driver in driving the vehicle so that the vehicle can travel in a target travel line set substantially in the center of the lane width.
A travel lane referred to as a carpool lane is employed in highways in large cities in the United States. The carpool lane is introduced to reduce a number of traveling vehicles or popularize environmentally-friendly vehicles (so called “eco-cars”) such as electrical vehicles.
More specifically, only ride-sharing vehicles or eco-cars are allowed to travel in the carpool lane. A vehicle occupied by a driver alone or a vehicle that does not meet predefined environmental criteria is forbidden from traveling in the carpool lane. Thus, there is a less number of traveling vehicles in the carpool lane, that is, the carpool lane is more vacant, as compared to in an ordinary lane. Therefore, use of the carpool lane may significantly reduce travel time.
For example, Patent Literature 1 proposes an assistance apparatus for assisting the driver in driving the vehicle also in such a carpool lane.
Patent Literature 1 JP-A-2010-128862
Technical Problem
The carpool lane is often provided parallel to an ordinary lane, where the carpool lane and the ordinary lane are partitioned by a lane line (hereinafter referred to as a lane partition line) therebetween. The lane partition line is basically formed of a plurality of (e.g., four) solid lines. The lane partition line is provided with entrances and exits spaced apart from each other by a predetermined distance. Each entrance and exit is marked by a single broken line, through which vehicles can move from the carpool lane to the ordinary lane or vice versa.
Typically, the carpool lane is broadened toward each entrance and exit (i.e., toward the ordinary lane). A lane width of each of entrance-and-exit lane sections of the carpool lane is greater than a lane width of each of lane sections of the carpool lane other than the entrance-and-exit lane sections. Therefore, when the vehicle is passing the entrance and exit of the carpool lane, the assistance apparatus determines that the lane width of the carpool lane is increased, which may cause the assistance apparatus to displace the target travel line toward the entrance and exit (toward the ordinary lane). When the vehicle has passed the entrance and exit of the carpool lane, then the assistance apparatus determines that the lane width of the carpool lane is decreased, which may cause the assistance apparatus to restore the target travel line. Accordingly, each time the vehicle passes the entrance and exit, the target travel line may be curved (become wavy), which may lead to unstable travelling of the vehicle.